EP2126403A1 - Method for adjusting damping characteristics in a shock absorber - Google Patents

Method for adjusting damping characteristics in a shock absorber

Info

Publication number
EP2126403A1
EP2126403A1 EP07861159A EP07861159A EP2126403A1 EP 2126403 A1 EP2126403 A1 EP 2126403A1 EP 07861159 A EP07861159 A EP 07861159A EP 07861159 A EP07861159 A EP 07861159A EP 2126403 A1 EP2126403 A1 EP 2126403A1
Authority
EP
European Patent Office
Prior art keywords
damping
main piston
pressure
flow
shock absorber
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP07861159A
Other languages
German (de)
French (fr)
Other versions
EP2126403B1 (en
EP2126403A4 (en
Inventor
Torkel Sintorn
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Ohlins Racing AB
Original Assignee
Ohlins Racing AB
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Ohlins Racing AB filed Critical Ohlins Racing AB
Publication of EP2126403A1 publication Critical patent/EP2126403A1/en
Publication of EP2126403A4 publication Critical patent/EP2126403A4/en
Application granted granted Critical
Publication of EP2126403B1 publication Critical patent/EP2126403B1/en
Active legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G17/00—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load
    • B60G17/06—Characteristics of dampers, e.g. mechanical dampers
    • B60G17/08—Characteristics of fluid dampers
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16F—SPRINGS; SHOCK-ABSORBERS; MEANS FOR DAMPING VIBRATION
    • F16F9/00—Springs, vibration-dampers, shock-absorbers, or similarly-constructed movement-dampers using a fluid or the equivalent as damping medium
    • F16F9/32—Details
    • F16F9/34—Special valve constructions; Shape or construction of throttling passages
    • F16F9/348—Throttling passages in the form of annular discs or other plate-like elements which may or may not have a spring action, operating in opposite directions or singly, e.g. annular discs positioned on top of the valve or piston body
    • F16F9/3485—Throttling passages in the form of annular discs or other plate-like elements which may or may not have a spring action, operating in opposite directions or singly, e.g. annular discs positioned on top of the valve or piston body characterised by features of supporting elements intended to guide or limit the movement of the annular discs
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16F—SPRINGS; SHOCK-ABSORBERS; MEANS FOR DAMPING VIBRATION
    • F16F9/00—Springs, vibration-dampers, shock-absorbers, or similarly-constructed movement-dampers using a fluid or the equivalent as damping medium
    • F16F9/32—Details
    • F16F9/44—Means on or in the damper for manual or non-automatic adjustment; such means combined with temperature correction
    • F16F9/46—Means on or in the damper for manual or non-automatic adjustment; such means combined with temperature correction allowing control from a distance, i.e. location of means for control input being remote from site of valves, e.g. on damper external wall
    • F16F9/461—Means on or in the damper for manual or non-automatic adjustment; such means combined with temperature correction allowing control from a distance, i.e. location of means for control input being remote from site of valves, e.g. on damper external wall characterised by actuation means
    • F16F9/462—Rotary actuation means
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G2202/00—Indexing codes relating to the type of spring, damper or actuator
    • B60G2202/20—Type of damper
    • B60G2202/24—Fluid damper
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G2500/00—Indexing codes relating to the regulated action or device
    • B60G2500/10—Damping action or damper
    • B60G2500/106—Damping action or damper duty rate

Definitions

  • the invention relates to a pressurized shock absorber intended for a vehicle, which basically comprises a damping medium-filled damping cylinder divided into two damping chambers, a compression chamber and a rebound chamber, by a piston fixed to a piston rod.
  • a restriction in the piston allows damping medium to pass between the chambers and valves serve to adjust the damping medium flow between the chambers, that is to say the damping characteristics of the shock absorber.
  • a pressurized shock absorber with positive pressure build-up always has a pressure greater than zero on both sides of the piston arranged in the damping cylinder, regardless of what conditions prevail. Pressurization on both sides of the piston is achieved in that a gas or spring-pressurized member, arranged in a pressurization reservoir, pressurizes a volume or space common to both damping chambers to a predetermined pressure.
  • RECORD COPY - TRANSLATION (Rule 12.4) separate adjusting elements are provided in order to adjust the flow in the flow ducts between the respective damping chambers and the pressurized common volume.
  • Said adjusting elements comprise one or more damping force-generating one-way valves (s) and a check valve, which opens as soon as the pressure in the common volume exceeds the pressure in the chamber having the lowest pressure at that particular instant. If a solid piston is used, the entire damping medium flow passes via the adjusting elements; see the applicant's own patent application EP 1659310 A2, for example, in which the adjusting element comprises a leakage flow valve, a main valve and a check valve. The leakage flow valve is arranged in parallel with the main valve.
  • the limitations of the TTX principle lie in the area of the flow ducts and its capacity to allow the passage of a sufficiently large damping medium flow.
  • This large damping medium flow is made possible by also introducing a flow, limited by the first flow-restricting element, via the main piston.
  • These first flow-restricting elements are preferably opened only when large pressure differentials occur between the damping chambers, that is to say the elements are high-speed damping elements.
  • a leakage or a bleed can also be introduced directly via the piston, which means that small pressure differentials over the piston, which occur in small, slow damping movements, can be evened out without the first flow-restricting elements in the main piston needing to open.
  • a device for adjusting this leakage flow in the piston and thereby controlling the low-speed damping, that is to say the damping of the vehicle's chassis/frame movements can be seen, for example in the applicant's own patent US 6,651,964 or in the patents US 5,277,283 and US 6,079,526. In these patents this leakage flow is adjusted by the restriction of a leakage flow duct, that is to say the flow gives an increase in force during the opening sequence which is relatively slow.
  • the first object is achieved in that two separate valves in the form of a high-speed valve and a low-speed valve are arranged in the main valve of the adjusting element.
  • the second problem has hitherto been solved only by the use of a shock absorber of conventional type, that is to say by using a shock absorber in which the pressure build-up occurs in series rather than in parallel, as with a TTX shock absorber.
  • This type of shock absorber carries disadvantages such as cavitation and a slow pressure build-up in the event of a large pressure gradient over the main piston and leads to difficulties in optimizing the damping characteristics on the compression and rebound stroke independently of one another.
  • the object of the present invention is to separate the adjustment of the damping characteristics for small or large pressure differentials over the piston.
  • the object of the invention is also to generate a sufficiently rapid build-up of force in the shock absorber even with small pressure differentials over the main piston.
  • a further object of the invention is to find a simple and economic solution to these problems.
  • the invention relates to a method of separating the adjustment of the damping characteristics for small or large pressure differentials over a main piston in a shock absorber with positive pressure build-up, intended for a vehicle.
  • the shock absorber comprises a damping medium-filled damping cylinder, divided into two damping chambers by the main piston.
  • Large pressure differentials over the main piston are caused by high speeds or large strokes on an axial movement of the main piston in the damping cylinder, in which the piston movement is preferably induced by movements between a vehicle wheel and its frame/chassis.
  • a pressure greater than zero is always generated on both sides of the main piston in that a pressure greater than zero is ensured in both of the damping chambers through pressurization of a first damping medium-filled space common to both damping chambers.
  • a pressurizing member pressurizes the common first space to a certain basic pressure, which varies between 5 and 30 bar.
  • At least a first and a second duct extending through the main piston are arranged in or on the main piston, the first duct being a leakage flow duct intended for low-speed damping and the second duct being defined, for example, by leaf shims, which open only at high speeds and/or under large strokes.
  • the adjusting elements comprise one or more damping force- generating one-way valve (s) of previously known type, each with its own check valve.
  • the damping characteristics are adjusted by the damping force- generating one-way valve (s) in the adjusting elements and/or by the flow through the second duct through the main piston.
  • small pressure differentials preferably between 0 and 5 bar, over the main piston, the damping characteristics are instead adjusted by a flow/leakage flow through the first duct, extending through the main piston.
  • the path of the flow/leakage flow is influenced in that the damping medium is prevented by the check valve (s) in the adjusting elements from flowing between the damping chambers via the separate flow ducts which connect the first space and the respective damping chambers together.
  • the adjustment of the damping characteristics is separated in that the check valve (s) in the adjusting elements are kept in a closed position by a force generated by a spring, when the pressure differentials over the main piston are small.
  • the force is equal to the force which the pressure differentials over the main piston generate on the check valve (s) through the change in pressure in the first common space .
  • the damping medium flow through the check valves is prevented in that the force acting on the check valves is selected so that a certain pressure differential over the main piston is required in order to open these.
  • the pressure differential over the main piston that is required for opening of the check valve is preferably determined by the basic pressure which prevails at least in the first common space and which is generated by the pressurizing member.
  • the spring is preloaded by a certain distance. This is done in order to create a function which requires a greater initial force for opening than for compression, which leads to the check valve opening without any delay when it actually opens, so that the adjustment of the damping characteristics occurs at precisely the desired instant.
  • the preloading of the spring can be modified by means of an adjusting element accessibly arranged for adjustment when the shock absorber is assembled into a unit, or can be performed when first fitting the adjusting element in the shock absorber.
  • the restriction of the damping medium flow in the duct in the main piston is adjustable.
  • the magnitude of the restriction is adjustable without affecting the flow through one-way valves of the adjusting elements.
  • the leakage flow via the main piston is preferably adjusted through the action of an adjusting bar, which is arranged in the piston rod and through a variation in its position increases or reduces the leakage flow via the piston.
  • the restriction of the damping medium flow through the piston is adjustable, the opening pressure of the check valve can be varied and ultimately adjusted to the preloading of the spring that generates the countervailing force on the check valve.
  • the description above therefore outlines a method in a pressurized shock absorber in which separate adjustment of the damping characteristics is possible for small or large pressure differentials over the piston.
  • This is achieved in that the damping characteristics for small pressure differentials are determined by a leakage flow through first ducts in the main piston and the damping characteristics for large pressure differentials are preferably determined by the flow through the adjusting elements and/or via second ducts in the main piston.
  • the invention also addresses the problem of generating a sufficiently rapid pressure build-up in the shock absorber even with small pressure differentials over the main piston, without detriment to the damping characteristics at high speeds. This is because in the event of larger pressure differentials over the main piston, damping medium flows through the check valve and pressurizes the chamber in which the pressure is lowest, that is to say the positive pressure build-up function with all its advantages is activated again.
  • Fig. 1 shows the shock absorber on a compressions stroke
  • Fig. 2 shows the shock absorber on a rebound stroke
  • Fig. 3 shows the adjusting elements
  • Fig. 4 shows the damping curves with speed and force on the axes
  • Figs. 1 and 2 parts of a shock absorber are generally denoted by 1.
  • the direction of flow for compression of the shock absorber, or the compression phase is indicated by the arrows C
  • the direction of flow for expansion of the shock absorber, often referred to as the rebound phase is indicated by the arrows R.
  • the shock absorber consists of a twin-tube shock absorber, the outer tube of which is indicated by 2 and the inner tube or damping cylinder by 3.
  • the tubes are arranged with an intervening gap 4 and at the first end of the shock absorber have passages 5, 6 for a medium contained in the shock absorber.
  • the shock absorber also comprises a main piston 7 and a piston rod 8.
  • the shock absorber is divided into two damping chambers, the compression space or the compression side being indicated by 9 and the rebound space or rebound side by 10.
  • the main piston 7 and the piston rod 8 are arranged in the damping chambers 9, 10 so that they are displaceable in the direction of the arrows C, R.
  • the piston 7 functions in a damping medium 13, which preferably consists of hydraulic oil, which may contain constituent additives of a type known in the art. Alternatively, glycol and/or water may be used as fluid.
  • the ends of the shock absorber are indicated by 12 and 12' .
  • the piston rod end 8a comprises a first fixing element 15, for example an end eye, which is intended for fastening the shock absorber to a part of the vehicle in question, moving in response to the running surface, preferably a wheel or runner.
  • the shock absorber has a second fixing element 15' , for example a cylinder head with associated top eye, which can be fastened to a chassis part of a vehicle in question.
  • the shock absorber is designed with two separate adjusting elements, which are generally denoted by 17 and 17' .
  • the first the adjusting element comprises a first damping force-generating one-way valve or compression-damping valve 18 and a first check valve 19.
  • the second adjusting element comprises a second damping force-generating one-way valve or rebound- damping valve 20 and a second check valve 21.
  • These damping force-generating one-way valves 18, 20 may in turn consist of one or more valves coupled in parallel and/or in series.
  • the shock absorber also has an accumulator or gas reservoir 22, which comprises a separating piston 23.
  • the gas reservoir encloses damping medium, preferably the aforesaid hydraulic oil with any additives or other fluid (see above).
  • the gas reservoir also comprises a second space 22b, which contains a second medium that is more compressible than the damping medium.
  • the compressible medium may consist of a gas, such as air, nitrogen gas or other gas with additives.
  • the pressurization means that the absolute pressure level is maintained at a level, for example at a level of approx. 2 bar or higher, sufficient to minimize the risk of cavitation due to the presence of restrictions in the relevant ducts.
  • the basic pressure is selected according to what damping characteristics are required of the shock absorber and what adjusting element 17, 17' are used.
  • Said adjusting elements 17, 17' also comprise flow ducts 27, 27', which connect said valves 18, 19, 20 and 21 and the space 22a in the reservoir 22 as well as the gap 4 and the spaces 9 and 10 in the shock absorber together.
  • the gap 4 and the space 10 may be regarded as a common volume.
  • the one-way valve 18 and the check valve 21 therefore form part of a first circuit Sl comprising the space 9, the connection 27', the space 22a, and the connection 27, and in which the gap 4 and the passage (s) 5 and 6 are connected like the space 10.
  • a second circuit S2 comprises the one-way valve 20 and the check valve 19, otherwise having the same connections .
  • the first damping force-generating one-way valve 18 is connected by its one end to the space 9 in the shock absorber, whilst the first check valve 19 is connected to the gap 4.
  • the second damping force-generating one- way valve 20 is connected to the gap 4, whilst the second check valve 21 is connected to the space 9.
  • Said first valves 18 and 19 are also connected via the connections 27' and 27 and the space 22a to the second valves 20 and 21.
  • the space 22a thus represents a volume common to both of the damping chambers 9, 10.
  • the shock absorber device 1 When the shock absorber device 1 operates in either stroke direction C, R, the main piston 7 moves in the damping cylinder 3 and in this way generates a pressure differential in the damping chambers 9, 10.
  • the pressure differentials create a damping medium flow, which on a compression stroke C is carried in the first circuit Sl, see the arrows in Fig. 1, and on a rebound stroke is carried in the second circuit S2, see the arrows in Fig. 2.
  • the magnitude of these flows Sl and S2 basically depends on the pressure differential P de i ta over the main piston 7 and the design of the adjusting elements 17 and 17' .
  • a p is equal to area of the main piston and A 3 is the piston rod area.
  • the pressure differential over the main piston 7 is adjusted by modifying its flow resistance.
  • the flow resistance is created by at least two ducts 38a, 38b with a certain area, which extend through the main piston 7. At least one duct 38a is covered by thin leaf valves 39.
  • the thin leaf valves 39 are designed to open first in the event of a certain large pressure differential P de i tar in order to adjust the damping characteristics of the shock absorber at extremely high speeds. This is done in order to limit the area of the flow ducts 27, 27' so that only a certain quantity of the damping medium flow is allowed to pass through to the adjusting elements 17, 17'. In the event of less extreme pressure differentials, the high-speed damping is only adjusted in the one-way valves 18, 20 of the adjusting elements 17, 17'.
  • the second duct or the restriction 38b preferably always has a certain flow area open, in order to allow a certain leakage flow or a bleed via the main piston.
  • This flow area is selected so that a certain quantity of damping medium manages to flow through the duct. This quantity is determined by the pressure differentials P de i ta over the piston 7 and these must not be too large, since the damping medium then instead takes the easiest way via a larger flow area, which is preferably via the one-way valves 18, 20 of the adjusting elements.
  • a leakage flow via the main piston 7 is therefore allowed only when the shock absorber moves with small, slow movements.
  • the leakage flow in Fig. 1 is shown fixed.
  • Fig. 2 shows a solution in which the leakage flow is adjustable by axial action, for example by means of an adjusting screw 43, on an adjusting bar 40 arranged in the piston rod 8.
  • adjusting bar 40 Owing to the upper design shape of the adjusting bar 40, for example a conical shape, different positions of the bar 40 in relation to the restriction 38b produce leakage flows of different magnitude .
  • Fig. 3 shows an enlarged view of the adjusting elements 17, 17', which are preferably arranged in or on the second fixing element 15' .
  • the adjusting elements 17 and 17' are of the same construction and reference will here only be made to one of the valves.
  • the valve 17 contains the one-way valve 18, through which damping medium flows in first ducts 34 away from the compression chamber 9 to the common space 22a.
  • the oneway valve 18 takes the form of a valve piston 28 with associated thin leaf valves 29 directly adjoining the first side 28a of the valve piston.
  • the valve piston 28 is fixed in a valve housing 30 between a cup 31 and an actuating member 32.
  • the actuating member may also comprise a duct (not shown) extending between the flow duct 27' and the common volume 22a, through which damping medium can flow in order to minimize the least perturbations in the valve.
  • the check valve 19 is arranged at the other side 28b of the piston.
  • the check valve 19 takes the form, for example, of a slide 36, which acts against a seat 37.
  • the slide 36 may take the form, for example, of a stiff leaf valve and is pressed by means of a force member, such as a spring 38, against the seat 37, preferably tightly against the other side 28b of the piston, in order to prevent a flow through the second through-ducts 33 of the valve piston 28 under certain predefined conditions.
  • the flow through the second through-duct 33 is prevented when the check valve 19 is closed.
  • the check valve 19 is closed as long as the pressure P r in the common volume 22a is less than the pressure Pi prevailing in the compression chamber 9 or when the pressure P r in the volume 22a gives a force F r on the slide 36 which is less than the spring force F s generated by the spring 37. Since the pressure in the damping chambers 8/9 in which the damping medium is compressed is greater than the pressure in the damping chambers 8/9 in which the chamber expands, the flow is led into the volume 22a through the one-way valve 18 in the adjusting element 17 described above and out of the volume 22a through the check valve 21 of the second adjusting element 17'. The opposite applies to the second adjusting element 17'. Since the adjusting elements 17, 17' are of the same construction, both of the check valves 19, 21 are therefore closed as long as the spring forces F 3 acting on them are greater than the force F r generated by the pressure P r in the volume 22a.
  • the compression flow C through the circuit Sl is capable of generating a certain increase in the pressure P r in the volume, since the damping medium volume expelled by the piston rod 8 is forced into the space 22a and compresses the compressible medium in the space 22b.
  • the pressure P r can also be expected to increase with the temperature, since the damping medium is expanded by a rise in the temperature and the space 22a accommodates even this increased volume.
  • the spring characteristics are preferably selected so that the spring is subject to a preload fs . Preloading the spring means that a greater initial force is required for opening than is required for compression F 3 , which leads to the check valve opening without delay when it actually opens.
  • the spring force F 3 is preferably selected so that the check valve is closed as long as the pressure in the volume 22a is between 5 and 30 bar, that is to say the spring constant k should lie between 0.5 and 10N/mm and the preload fs should be between 0.5 and 5 mm. These values will obviously vary depending on the magnitude of the leakage flow via the main piston 7.
  • a first embodiment see Fig. 3 valve 17
  • preloading is performed by introducing a distance piece 41 with a certain predetermined height into the cup 31.
  • the cup 31 is an exchangeable component having a certain wall height.
  • the position of the valve piston 28 in the valve housing 30 is vertically adjustable, for example in that a threaded union 42 couples the piston 38 to the valve housing 30 or the cup 31 and that the position of the piston can be adjusted by means of an external adjusting element, which may be integrally formed with the actuating member 32 fixed to the piston.
  • the preloading of the spring 37 can be adjusted by means of an adjusting element accessibly arranged for adjustment when the shock absorber is assembled into a unit.
  • Fig. 4 shows the damping curves for the shock absorber according to the invention.
  • the curves are plotted with the piston rod speed v on the horizontal axis and the force F on the vertical axis.
  • the gradient of the damping curves therefore determines how rapidly the force is built up and this build-up of force is determined by the nature of the check valves 19, 21 or by the leakage flow through the main piston 7.
  • the relationship of the pressure gradient Delta P to the speed of movement v is in turn also adjustable by adjusting the leakage flow through a restriction 38b over the main piston 7.
  • the transition between parallel and serial flow occurs at a higher piston rod speed v, due to the fact that delta P is not attained until the piston speed is so great that the restriction 38b, despite its size, can no longer allow all the damping medium to pass through. If, on the other hand, the preloading fs is high or the spring constant Fs is large, the transition then also occurs at a higher piston speed, since a greater pressure gradient Delta P is required in order to open the check valve.
  • Fig. 4 illustrates this in that the damping curve slope is steeper up to a certain piston rod speed v. Since the nature of the check valve 18, 21 or the restriction 38b in the main piston 7 has an effect on this, it is possible to control the damping constants separately, which affords a facility for controlling the chassis movements on a vehicle, that is to say low frequencies and low piston speeds, separately from wheel movements, that is to say high frequencies and high piston speeds.

Abstract

The invention relates to a method in a shock absorber (1) of separating the adjustment of the damping characteristics for small or large pressure differentials over the main piston (7). Arranged in the shock absorber is a damping medium-filled damping cylinder, divided into two damping chambers (8, 9) by a main piston (7) fixed to a piston rod (8). At least one duct (38a, 38b) is arranged in the main piston (7) or in the piston rod (8) in order to allow a certain damping medium flow between the damping chambers (8, 9). Also connected to the shock absorber (1) is a pressurized member (23), arranged in a pressurization reservoir (22). The pressurized member (23) pressurizes a volume (22a), common to both of the damping chambers (8, 9), to a certain basic pressure, which varies between 5 and 30 bar. This common volume (22a) is connected by separate flow ducts (27, 27') to the respective damping chambers (8, 9). Two separate adjusting elements (17, 17') are arranged between the common volume (22a) and the respective damping chambers (8, 9). These comprise one or more damping force- generating one-way valve (s) (18, 20) of a type known in the art and a check valve (19, 21). The check valve (19, 21) is subjected to and kept in a closed position by a force (Fs). With small pressure differentials over the main piston (7), the damping medium is prevented from flowing between the damping chambers (8, 9) via the adjusting elements (17, 17') but is forced to flow through the duct (38b) in or on the main piston.

Description

METHOD FOR ADJUSTING DAMPING CHARACTERISTICS IN A SHOCK
ABSORBER
Technical field
The invention relates to a pressurized shock absorber intended for a vehicle, which basically comprises a damping medium-filled damping cylinder divided into two damping chambers, a compression chamber and a rebound chamber, by a piston fixed to a piston rod. A restriction in the piston allows damping medium to pass between the chambers and valves serve to adjust the damping medium flow between the chambers, that is to say the damping characteristics of the shock absorber.
Background of the invention
In order to avoid cavitation in a pressurized shock absorber of the aforementioned type whilst retaining a large adjustment range and a rapid response time even with large shock absorber strokes and/or high piston speeds, that is to say large pressure differentials over the piston, use is currently made of a principle which is referred to by the applicant as positive pressure build-up or TTX. A pressurized shock absorber with positive pressure build-up always has a pressure greater than zero on both sides of the piston arranged in the damping cylinder, regardless of what conditions prevail. Pressurization on both sides of the piston is achieved in that a gas or spring-pressurized member, arranged in a pressurization reservoir, pressurizes a volume or space common to both damping chambers to a predetermined pressure. Pressurization of the damping medium in the body of the shock absorber then occurs parallel with the stroke movement, which is axial in relation to the damping cylinder. The two damping chambers with the common volume are coupled together by means of a first flow duct between the compression chamber and the common volume and a second flow duct between the rebound chamber and the common volume. Two
RECORD COPY - TRANSLATION (Rule 12.4) separate adjusting elements are provided in order to adjust the flow in the flow ducts between the respective damping chambers and the pressurized common volume. Said adjusting elements comprise one or more damping force-generating one-way valves (s) and a check valve, which opens as soon as the pressure in the common volume exceeds the pressure in the chamber having the lowest pressure at that particular instant. If a solid piston is used, the entire damping medium flow passes via the adjusting elements; see the applicant's own patent application EP 1659310 A2, for example, in which the adjusting element comprises a leakage flow valve, a main valve and a check valve. The leakage flow valve is arranged in parallel with the main valve.
In a vehicle intended to absorb rapid movements and large impacts, caused by the nature of the running surface with its stones, holes and large irregularities, the limitations of the TTX principle lie in the area of the flow ducts and its capacity to allow the passage of a sufficiently large damping medium flow. This large damping medium flow is made possible by also introducing a flow, limited by the first flow-restricting element, via the main piston. These first flow-restricting elements are preferably opened only when large pressure differentials occur between the damping chambers, that is to say the elements are high-speed damping elements. A leakage or a bleed can also be introduced directly via the piston, which means that small pressure differentials over the piston, which occur in small, slow damping movements, can be evened out without the first flow-restricting elements in the main piston needing to open. A device for adjusting this leakage flow in the piston and thereby controlling the low-speed damping, that is to say the damping of the vehicle's chassis/frame movements, can be seen, for example in the applicant's own patent US 6,651,964 or in the patents US 5,277,283 and US 6,079,526. In these patents this leakage flow is adjusted by the restriction of a leakage flow duct, that is to say the flow gives an increase in force during the opening sequence which is relatively slow.
Easy and cost-effective adjustment of the low-speed damping separately from the high-speed damping, that is to say adjusting the damping characteristics for small or large pressure differentials over the main piston separately from one another, has proved to be a problem in a vehicle shock absorber with positive pressure build-up.
With small strokes and a slight pressure differential over the main piston, it can also be a problem, in a shock absorber with positive pressure build-up, to generate a sufficiently rapid increase in force, that is to say a high damping constant, also at the start of the stroke.
In the prior art, for example in EP 1659310 A2, the first object is achieved in that two separate valves in the form of a high-speed valve and a low-speed valve are arranged in the main valve of the adjusting element. This implies a complicated and expensive main valve with many parts. The second problem has hitherto been solved only by the use of a shock absorber of conventional type, that is to say by using a shock absorber in which the pressure build-up occurs in series rather than in parallel, as with a TTX shock absorber. This type of shock absorber carries disadvantages such as cavitation and a slow pressure build-up in the event of a large pressure gradient over the main piston and leads to difficulties in optimizing the damping characteristics on the compression and rebound stroke independently of one another. Object of the invention
The object of the present invention is to separate the adjustment of the damping characteristics for small or large pressure differentials over the piston.
The object of the invention is also to generate a sufficiently rapid build-up of force in the shock absorber even with small pressure differentials over the main piston.
A further object of the invention is to find a simple and economic solution to these problems.
Summary of the invention The invention relates to a method of separating the adjustment of the damping characteristics for small or large pressure differentials over a main piston in a shock absorber with positive pressure build-up, intended for a vehicle. The shock absorber comprises a damping medium-filled damping cylinder, divided into two damping chambers by the main piston. Large pressure differentials over the main piston are caused by high speeds or large strokes on an axial movement of the main piston in the damping cylinder, in which the piston movement is preferably induced by movements between a vehicle wheel and its frame/chassis. With a positive pressure build-up, a pressure greater than zero is always generated on both sides of the main piston in that a pressure greater than zero is ensured in both of the damping chambers through pressurization of a first damping medium-filled space common to both damping chambers. A pressurizing member pressurizes the common first space to a certain basic pressure, which varies between 5 and 30 bar. At least a first and a second duct extending through the main piston are arranged in or on the main piston, the first duct being a leakage flow duct intended for low-speed damping and the second duct being defined, for example, by leaf shims, which open only at high speeds and/or under large strokes. Two separate adjusting elements are arranged in separate flow ducts which connect the first space and the respective damping chambers together. The adjusting elements comprise one or more damping force- generating one-way valve (s) of previously known type, each with its own check valve. With large pressure differentials over the main piston, which also give an increased flow through the flow ducts and an increased pressure in the first common space, the damping characteristics are adjusted by the damping force- generating one-way valve (s) in the adjusting elements and/or by the flow through the second duct through the main piston. With small pressure differentials, preferably between 0 and 5 bar, over the main piston, the damping characteristics are instead adjusted by a flow/leakage flow through the first duct, extending through the main piston. The path of the flow/leakage flow is influenced in that the damping medium is prevented by the check valve (s) in the adjusting elements from flowing between the damping chambers via the separate flow ducts which connect the first space and the respective damping chambers together.
In a first embodiment the adjustment of the damping characteristics is separated in that the check valve (s) in the adjusting elements are kept in a closed position by a force generated by a spring, when the pressure differentials over the main piston are small. The force is equal to the force which the pressure differentials over the main piston generate on the check valve (s) through the change in pressure in the first common space .
In a further embodiment the damping medium flow through the check valves is prevented in that the force acting on the check valves is selected so that a certain pressure differential over the main piston is required in order to open these. The pressure differential over the main piston that is required for opening of the check valve is preferably determined by the basic pressure which prevails at least in the first common space and which is generated by the pressurizing member.
In a third embodiment of the invention the spring is preloaded by a certain distance. This is done in order to create a function which requires a greater initial force for opening than for compression, which leads to the check valve opening without any delay when it actually opens, so that the adjustment of the damping characteristics occurs at precisely the desired instant.
The preloading of the spring can be modified by means of an adjusting element accessibly arranged for adjustment when the shock absorber is assembled into a unit, or can be performed when first fitting the adjusting element in the shock absorber.
In a further embodiment the restriction of the damping medium flow in the duct in the main piston is adjustable. The magnitude of the restriction is adjustable without affecting the flow through one-way valves of the adjusting elements. The leakage flow via the main piston is preferably adjusted through the action of an adjusting bar, which is arranged in the piston rod and through a variation in its position increases or reduces the leakage flow via the piston. Where the restriction of the damping medium flow through the piston is adjustable, the opening pressure of the check valve can be varied and ultimately adjusted to the preloading of the spring that generates the countervailing force on the check valve.
The description above therefore outlines a method in a pressurized shock absorber in which separate adjustment of the damping characteristics is possible for small or large pressure differentials over the piston. This is achieved in that the damping characteristics for small pressure differentials are determined by a leakage flow through first ducts in the main piston and the damping characteristics for large pressure differentials are preferably determined by the flow through the adjusting elements and/or via second ducts in the main piston. The invention also addresses the problem of generating a sufficiently rapid pressure build-up in the shock absorber even with small pressure differentials over the main piston, without detriment to the damping characteristics at high speeds. This is because in the event of larger pressure differentials over the main piston, damping medium flows through the check valve and pressurizes the chamber in which the pressure is lowest, that is to say the positive pressure build-up function with all its advantages is activated again.
The invention will be described in more detail below, with reference to the drawings attached.
Brief description of the drawings
Fig. 1 shows the shock absorber on a compressions stroke
Fig. 2 shows the shock absorber on a rebound stroke
Fig. 3 shows the adjusting elements
Fig. 4 shows the damping curves with speed and force on the axes
Detailed description of the invention
In Figs. 1 and 2 parts of a shock absorber are generally denoted by 1. In Fig. 1 the direction of flow for compression of the shock absorber, or the compression phase, is indicated by the arrows C and in Fig. 2 the direction of flow for expansion of the shock absorber, often referred to as the rebound phase, is indicated by the arrows R. In the exemplary embodiment the shock absorber consists of a twin-tube shock absorber, the outer tube of which is indicated by 2 and the inner tube or damping cylinder by 3. The tubes are arranged with an intervening gap 4 and at the first end of the shock absorber have passages 5, 6 for a medium contained in the shock absorber. The shock absorber also comprises a main piston 7 and a piston rod 8.
The shock absorber is divided into two damping chambers, the compression space or the compression side being indicated by 9 and the rebound space or rebound side by 10. The main piston 7 and the piston rod 8 are arranged in the damping chambers 9, 10 so that they are displaceable in the direction of the arrows C, R. The piston 7 functions in a damping medium 13, which preferably consists of hydraulic oil, which may contain constituent additives of a type known in the art. Alternatively, glycol and/or water may be used as fluid.
The ends of the shock absorber are indicated by 12 and 12' . The piston rod end 8a comprises a first fixing element 15, for example an end eye, which is intended for fastening the shock absorber to a part of the vehicle in question, moving in response to the running surface, preferably a wheel or runner. At the upper end 2a of the outer tube 2, the shock absorber has a second fixing element 15' , for example a cylinder head with associated top eye, which can be fastened to a chassis part of a vehicle in question.
The shock absorber is designed with two separate adjusting elements, which are generally denoted by 17 and 17' . The first the adjusting element comprises a first damping force-generating one-way valve or compression-damping valve 18 and a first check valve 19. The second adjusting element comprises a second damping force-generating one-way valve or rebound- damping valve 20 and a second check valve 21. These damping force-generating one-way valves 18, 20 may in turn consist of one or more valves coupled in parallel and/or in series.
According to Figs. 1 and 2 the shock absorber also has an accumulator or gas reservoir 22, which comprises a separating piston 23. In a first space 22a the gas reservoir encloses damping medium, preferably the aforesaid hydraulic oil with any additives or other fluid (see above). The gas reservoir also comprises a second space 22b, which contains a second medium that is more compressible than the damping medium. The compressible medium may consist of a gas, such as air, nitrogen gas or other gas with additives. By filling the second space with compressible medium, a basic pressure is generated, which acts on the damping medium in the space 22a.
With a large pressure differential on the main piston 7, the pressurization means that the absolute pressure level is maintained at a level, for example at a level of approx. 2 bar or higher, sufficient to minimize the risk of cavitation due to the presence of restrictions in the relevant ducts. The basic pressure is selected according to what damping characteristics are required of the shock absorber and what adjusting element 17, 17' are used.
Said adjusting elements 17, 17' also comprise flow ducts 27, 27', which connect said valves 18, 19, 20 and 21 and the space 22a in the reservoir 22 as well as the gap 4 and the spaces 9 and 10 in the shock absorber together. The gap 4 and the space 10 may be regarded as a common volume. The one-way valve 18 and the check valve 21 therefore form part of a first circuit Sl comprising the space 9, the connection 27', the space 22a, and the connection 27, and in which the gap 4 and the passage (s) 5 and 6 are connected like the space 10. A second circuit S2 comprises the one-way valve 20 and the check valve 19, otherwise having the same connections .
The first damping force-generating one-way valve 18 is connected by its one end to the space 9 in the shock absorber, whilst the first check valve 19 is connected to the gap 4. The second damping force-generating one- way valve 20 is connected to the gap 4, whilst the second check valve 21 is connected to the space 9. Said first valves 18 and 19 are also connected via the connections 27' and 27 and the space 22a to the second valves 20 and 21. The space 22a thus represents a volume common to both of the damping chambers 9, 10.
When the shock absorber device 1 operates in either stroke direction C, R, the main piston 7 moves in the damping cylinder 3 and in this way generates a pressure differential in the damping chambers 9, 10. The pressure differentials create a damping medium flow, which on a compression stroke C is carried in the first circuit Sl, see the arrows in Fig. 1, and on a rebound stroke is carried in the second circuit S2, see the arrows in Fig. 2.
The magnitude of these flows Sl and S2 basically depends on the pressure differential Pdeita over the main piston 7 and the design of the adjusting elements 17 and 17' .
The pressure differential Pdeita over the main piston is Pdeita =Pi- P2 , where pi is the pressure in the damping chamber with compressed volume, that is to say Pi=Fl/ (Ap+ A3), and p2 is the pressure in the damping chamber with expanded volume, that is to say p2=F2/ Ap. Ap is equal to area of the main piston and A3 is the piston rod area. The pressure differential over the main piston 7 is adjusted by modifying its flow resistance. The flow resistance is created by at least two ducts 38a, 38b with a certain area, which extend through the main piston 7. At least one duct 38a is covered by thin leaf valves 39. The thin leaf valves 39 are designed to open first in the event of a certain large pressure differential Pdeitar in order to adjust the damping characteristics of the shock absorber at extremely high speeds. This is done in order to limit the area of the flow ducts 27, 27' so that only a certain quantity of the damping medium flow is allowed to pass through to the adjusting elements 17, 17'. In the event of less extreme pressure differentials, the high-speed damping is only adjusted in the one-way valves 18, 20 of the adjusting elements 17, 17'.
The second duct or the restriction 38b preferably always has a certain flow area open, in order to allow a certain leakage flow or a bleed via the main piston. This flow area is selected so that a certain quantity of damping medium manages to flow through the duct. This quantity is determined by the pressure differentials Pdeita over the piston 7 and these must not be too large, since the damping medium then instead takes the easiest way via a larger flow area, which is preferably via the one-way valves 18, 20 of the adjusting elements. A leakage flow via the main piston 7 is therefore allowed only when the shock absorber moves with small, slow movements. The leakage flow in Fig. 1 is shown fixed.
Fig. 2 shows a solution in which the leakage flow is adjustable by axial action, for example by means of an adjusting screw 43, on an adjusting bar 40 arranged in the piston rod 8. Owing to the upper design shape of the adjusting bar 40, for example a conical shape, different positions of the bar 40 in relation to the restriction 38b produce leakage flows of different magnitude .
Fig. 3 shows an enlarged view of the adjusting elements 17, 17', which are preferably arranged in or on the second fixing element 15' . The adjusting elements 17 and 17' are of the same construction and reference will here only be made to one of the valves. The valve 17 contains the one-way valve 18, through which damping medium flows in first ducts 34 away from the compression chamber 9 to the common space 22a. The oneway valve 18 takes the form of a valve piston 28 with associated thin leaf valves 29 directly adjoining the first side 28a of the valve piston. The valve piston 28 is fixed in a valve housing 30 between a cup 31 and an actuating member 32. The actuating member may also comprise a duct (not shown) extending between the flow duct 27' and the common volume 22a, through which damping medium can flow in order to minimize the least perturbations in the valve. The check valve 19 is arranged at the other side 28b of the piston. The check valve 19 takes the form, for example, of a slide 36, which acts against a seat 37. The slide 36 may take the form, for example, of a stiff leaf valve and is pressed by means of a force member, such as a spring 38, against the seat 37, preferably tightly against the other side 28b of the piston, in order to prevent a flow through the second through-ducts 33 of the valve piston 28 under certain predefined conditions.
The flow through the second through-duct 33 is prevented when the check valve 19 is closed. The check valve 19 is closed as long as the pressure Pr in the common volume 22a is less than the pressure Pi prevailing in the compression chamber 9 or when the pressure Pr in the volume 22a gives a force Fr on the slide 36 which is less than the spring force Fs generated by the spring 37. Since the pressure in the damping chambers 8/9 in which the damping medium is compressed is greater than the pressure in the damping chambers 8/9 in which the chamber expands, the flow is led into the volume 22a through the one-way valve 18 in the adjusting element 17 described above and out of the volume 22a through the check valve 21 of the second adjusting element 17'. The opposite applies to the second adjusting element 17'. Since the adjusting elements 17, 17' are of the same construction, both of the check valves 19, 21 are therefore closed as long as the spring forces F3 acting on them are greater than the force Fr generated by the pressure Pr in the volume 22a.
The compression flow C through the circuit Sl is capable of generating a certain increase in the pressure Pr in the volume, since the damping medium volume expelled by the piston rod 8 is forced into the space 22a and compresses the compressible medium in the space 22b. The pressure Pr can also be expected to increase with the temperature, since the damping medium is expanded by a rise in the temperature and the space 22a accommodates even this increased volume.
Through the right choice of spring characteristics for the spring 37, however, it is therefore possible to create a condition which means that, with small pressure differentials, for example between 0 and 5 bar, over the main piston 7, damping medium will be accumulated in the volume/the space 22a and the damping characteristics will be determined solely by the adjustable leakage flow in the main piston 7.
The spring characteristics are preferably selected so that the spring is subject to a preload fs . Preloading the spring means that a greater initial force is required for opening than is required for compression F3, which leads to the check valve opening without delay when it actually opens. The spring force F3 is preferably selected so that the check valve is closed as long as the pressure in the volume 22a is between 5 and 30 bar, that is to say the spring constant k should lie between 0.5 and 10N/mm and the preload fs should be between 0.5 and 5 mm. These values will obviously vary depending on the magnitude of the leakage flow via the main piston 7.
In a first embodiment, see Fig. 3 valve 17, preloading is performed by introducing a distance piece 41 with a certain predetermined height into the cup 31. In a second embodiment (not shown) the cup 31 is an exchangeable component having a certain wall height. In a third embodiment, see Fig. 3 valve 17', the position of the valve piston 28 in the valve housing 30 is vertically adjustable, for example in that a threaded union 42 couples the piston 38 to the valve housing 30 or the cup 31 and that the position of the piston can be adjusted by means of an external adjusting element, which may be integrally formed with the actuating member 32 fixed to the piston. With the third embodiment, therefore, the preloading of the spring 37 can be adjusted by means of an adjusting element accessibly arranged for adjustment when the shock absorber is assembled into a unit.
With large pressure differentials over the main piston 7, the check valves 19, 21 open and damping medium flows into and pressurizes the chamber in which the pressure is lowest, that is to say the positive pressure build-up function is activated again and cavitation can be avoided whilst reducing the response time for the larger pressure build-up of the shock absorber.
Fig. 4 shows the damping curves for the shock absorber according to the invention. The curves are plotted with the piston rod speed v on the horizontal axis and the force F on the vertical axis. The gradient of the damping curves therefore determines how rapidly the force is built up and this build-up of force is determined by the nature of the check valves 19, 21 or by the leakage flow through the main piston 7.
A transition therefore occurs between serial flow and parallel flow, denoted in Fig. 4 by F0, when the check valve 19, 21 is opened. Just when this occurs depends on the preloading fs of the check valve or its spring constant k, which creates a pressure gradient Delta P over the check valve. The relationship of the pressure gradient Delta P to the speed of movement v is in turn also adjustable by adjusting the leakage flow through a restriction 38b over the main piston 7.
If the restriction 38b over the main piston is designed so that a lot of damping medium can flow via the main piston, the transition between parallel and serial flow occurs at a higher piston rod speed v, due to the fact that delta P is not attained until the piston speed is so great that the restriction 38b, despite its size, can no longer allow all the damping medium to pass through. If, on the other hand, the preloading fs is high or the spring constant Fs is large, the transition then also occurs at a higher piston speed, since a greater pressure gradient Delta P is required in order to open the check valve.
The effect of having a serial flow for low speeds but parallel flows at higher piston speeds is that with the serial flow the damping constant is higher than with the parallel flow. Fig. 4 illustrates this in that the damping curve slope is steeper up to a certain piston rod speed v. Since the nature of the check valve 18, 21 or the restriction 38b in the main piston 7 has an effect on this, it is possible to control the damping constants separately, which affords a facility for controlling the chassis movements on a vehicle, that is to say low frequencies and low piston speeds, separately from wheel movements, that is to say high frequencies and high piston speeds.
The invention is not limited to the exemplary embodiment demonstrated above, but may be modified without departing from the scope of the following patent claims and the idea of the invention.

Claims

Patent claims
1. Method of separating the adjustment of the damping characteristics for small or large pressure differentials over a main piston (7) in a shock absorber (1) with positive pressure build-up, in which a pressure greater than zero is ensured on both sides of the main piston (7), the shock absorber comprising a damping medium-filled damping cylinder (3) , divided into two damping chambers (8, 9) by the main piston
(7), in or one which at least a first and a second duct
(38b, 38a) are arranged extending through the main piston (7), and a pressure greater than zero being ensured in the damping chambers (8, 9) through the pressurization of a first damping medium-filled space (22a), common to both the damping chambers (8, 9) and connected to both of the damping chambers (8, 9), to a certain basic pressure (Pr), and two separate adjusting elements (17, 17') comprising one or more damping force-generating one-way valve (s) (18, 20), each with its own check valve (19, 21), being arranged in separate flow ducts (27, 27') which connect the first space (22a) and the respective damping chambers (8, 9) together, characterized in that for large pressure differentials over the main piston (7), which also generate an increased pressure in the first common space (22a) , the damping characteristics are adjusted by the damping force-generating one-way valve (s) (18, 20) in the adjusting elements (17, 17') and for small pressure differentials over the main piston (7) the damping characteristics are instead adjusted by a flow/bleed flow through the first duct (38b) in or on the main piston (7) in that the damping medium is prevented by the check valve (s) (19, 21) in the adjusting elements (17, 17') from flowing between the damping chambers (8, 9) via the separate flow ducts (27, 27') which connect the first space (22a) and the respective damping chambers (8, 9) together.
2. Method according to Claim 1, characterized in that the check valve (s) (19, 21) in the adjusting elements (17, 17') are subjected to and kept in a closed position by a force (F3) , which is generated by a spring (37) and which is equal to the force which the small pressure differentials over the main piston (7) generate on the check valve (s) (19, 21) through the change in pressure in the first common space (22a) .
3. Method according to Claim 1 or 2, characterized in that the small pressure differentials over the main piston (7) are between 0 and 5 bar.
4. Method according to Claim 2 or 3, characterized in that the damping medium flow through the check valves (19, 21) is prevented in that the force (F3) acting on the check valves (19, 21) is selected so that a certain pressure differential over the main piston (7) is required in order to open these.
5. Method according to Claim 4, characterized in that the pressure differential over the main piston (7) that is required in order to open the check valve (19, 21) is determined by the basic pressure (Pr) which prevails at least in the common volume (22a) and which is generated by the pressurizing member (23) .
6. Method according to any one of the preceding Claims, characterized in that the spring (37) is preloaded by a certain distance (fs) in order to create a function which requires a greater initial force for opening than for compression.
7. Method according to Claim 6, characterized in that the preloading (fs) of the spring (38) can be adjusted by means of an adjusting element (32) accessibly arranged for adjustment when the shock absorber (1) is assembled into a unit.
8. Method according to Claim 6, characterized in that a predetermined preloading (fs) of the spring (38) is performed when first fitting the adjusting element (17, 17') in the shock absorber.
9. Method according to any one of the preceding Claims, characterized in that the damping medium flow through the duct (38b) is adjustable.
10. Method according to Claim 9, characterized in that the damping medium flow through the duct (38b) is adjusted through the action of an adjusting bar (40), which is arranged in the piston rod (8) and which through its design shape and a variation in its position increases or reduces the leakage flow via the main piston (7 ) .
EP07861159.7A 2006-12-26 2007-12-20 Method for adjusting damping characteristics in a shock absorber Active EP2126403B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE0602821A SE532119C2 (en) 2006-12-26 2006-12-26 Procedure for adjusting the damping properties of a shock absorber
PCT/SE2007/051064 WO2008079093A1 (en) 2006-12-26 2007-12-20 Method for adjusting damping characteristics in a shock absorber

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EP2126403A1 true EP2126403A1 (en) 2009-12-02
EP2126403A4 EP2126403A4 (en) 2010-02-10
EP2126403B1 EP2126403B1 (en) 2013-05-22

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Also Published As

Publication number Publication date
EP2126403B1 (en) 2013-05-22
SE0602821L (en) 2008-06-27
WO2008079093A1 (en) 2008-07-03
EP2126403A4 (en) 2010-02-10
SE532119C2 (en) 2009-10-27

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